I want to use the Teensy++ 2 to run a chessboard with 64 LEDS and 64 reed switches. The centepede shield: http://docs.macetech.com/doku.php/centipede_shield seems an ideal solution, especially as you can link two to address 128. it It uses the Wire I2C interface on analog pins 4 and 5 to provide 64 general purpose I/O pins. (x2) so I get massive addressing for only 2 pins with the added bonus that you connect using a ribbon cable and it has built in resistors.

It is designed to stack on a standard uno type board, however I want to use the Teensy because that can communicate using serial USB and keyboard at the same time.

So my question is, which pins represent the "Wire I2C interface on analog pins 4 and 5 " and can i just solder connections of two centipedes in a daisy chain arrangement?

The MCP23017 I2C interface can have up to 8 unique bus addresses. The Centipede Shield uses X00 to X11, where X is the value of the ADDRESS jumper. This allows the Centipede Shield address space to be shifted by four places, either to prevent interference on the I2C bus with another device, or to allow two Centipede Shields to coexist.

so it seems that you can use 2 shield simultaneously and just solder them together as the I2C addressing takes care of selecting the right shield.

That's correct. You can string the shields together with a few wires, connect the SDA and SCL in parallel. I don't have a Teensy to test, so there is no Centipede Library for it...but you should be able to get it working quickly, the library is merely convenient.

A chess board is also the perfect layout for a matrix arrangement...you may not really need that many channels. The reed switches could easily be read with 16 pins.